This invention relates to a method and a device for printing objects, more particularly for printing the surface of three-dimensional objects.
A practical application intended by the invention is the application of a decorative coating on the casing of portable telephones, in particular on the front side of GSM devices. It is known that the front side of such devices comprises inwardly-directed parts, such as, for example, the seats of the push-buttons. Generally, these front sides are provided with a colour or ink coating by means of a paint spraying technique. A disadvantage of this technique consists in that it is difficult to provide the inward-bent parts with ink and/or colour. This becomes even more difficult when the coating must not consist of only one and the same colour layer and, for example, it is desired to form images on the front side, as then it is necessary to work with masks. Another disadvantage consists in that this technique is little environment-friendly, as a large part of the colour or ink will get beside the object.
The present invention in the first place aims at a method and a device which are particularly suited for printing three-dimensional objects. More particularly, it aims at a technique whereby the aforementioned disadvantages when printing the front side of GSM devices and similar, are excluded.
To this aim, the invention concerns a method for printing objects, with as a characteristic that it at least consists in, on one hand, the application of printing ink on a carrier consisting of a flexible layer-shaped material and, on the other hand, transferring the printing ink to the object to be printed, by bringing said carrier and the object into mutual contact and by pressing-on said carrier, by means of supplementary pressing means, at least partially around the object to be printed.
By using a flexible carrier, it is obtained that the carrier easily can assume the shape of the surface to be printed and, by moreover applying supplementary pressing means therewith, a complete pressing-on can be guaranteed.
Preferably, for the supplementary pressing means use is made of a fluid pressure, more particularly air pressure, with which a pressure is exerted on the side of the carrier which is opposite to the side which is brought into contact with the object to be printed.
According to another possibility, supplementary pressing means of mechanical nature are applied, such as a counterform of the object to be printed, with which the carrier can be pressed against the object.
In the most preferred form of embodiment, the aforementioned two kinds of pressing means will be combined, which, in the first place, is useful when printing the front side of a portable telephone. By this combination, it is achieved that the carrier can be pressed into small, relatively deep indentations by means of the counterform, whereas by the pressing, realized by means of the compressed air, on one hand, always a perfect pressing over the entire surface to be printed is guaranteed, whereas, on the other hand, also the bent lateral edges of the object can be printed which are difficult to reach by means of a counterform.
In a preferred form of embodiment, the image to be printed is applied on the carrier in two-dimensional condition and then, by deformation of the carrier, printed on the object in three-dimensional condition. This technique allows for that the application of the image which can consist of a figure as well as of an even coating of one and the same colour or similar, can easily be realized.
In a practical form of embodiment, the carrier will be stretched at least during the application of the printing ink, in such a manner that during the application a flat substructure is offered. According to a variant, however, it is not excluded to provide a support surface under this carrier during the application of the printing ink, whether or not combined with the stretching of the carrier.
Preferably, the carrier will also be stretched during the actual printing, for example, by pressing the object to be printed over a well-defined distance into the plane of the carrier.
More particularly, it is preferred that the carrier during the application of the printing ink and the actual printing is stretched in opposite direction, whereby it is displaced over approximately the same distance, and even better is displaced in such a manner that approximately the same extension at the location of the printed image takes place, with the advantage that there is almost no size difference between the image applied on the carrier and the printed image.
Practically, a carrier will be applied showing a contact surface consisting of a colour- or ink-repellent material. According to a particular characteristic of the invention, to this aim use will be made of a silicone mat or a flexible layer of material based on silicones. Such material offers the advantage that it is very flexible and at the same time will easily release the printing ink during printing.
According to a particular aspect of the invention, the printing ink is provided on the support by means of a printer. As a result of this, forming different images and rapidly switching over from one image to the other is rendered very easy, simply by controlling the printer.
The invention also relates to a device for realizing the aforementioned method, with as a characteristic that it at least consists of a carrier of a flexible layer-shaped material; means for applying printing ink on the carrier; means for transferring the printing ink to the object to be printed, said means consisting of a displacement mechanism for bringing said carrier and the object into mutual contact; and supplementary pressing means which cooperate with the carrier and allow to press on the latter, at least partially around the object to be printed.